Karthik R
Hello If you are trying to run a multiphase analysis, you can use the VoF approach if the two phases are immiscible. You should be able to patch a spherical region for the gas in your 2D domain.
For turbulent flow, check your overall Reynolds number and activate one of the turbulent viscous model (note: the current versions have the turbulence model enabled by default).
If you do not wish to consider the interactions between the gas bubble and the fluid (gas bubble is just a rigid solid sphere), you can simply remove the spherical region from the analysis). This would be similar to flow over a bluff body. However, this might not be what you are looking for.